Konst der zeevaert.[Rotterdam?, ca. 1649?]. Folio (32 x 21 cm). Manuscript in Dutch, written in a clear upright gothic cursive hand in brown ink on paper, with 41 illustrations (an equinoctial compass sundial, quadrants and numerous diagrams, more than half in colour and a few full-page or nearly full-page); 5 coloured cartouches with scales, brief tables, etc.; and more extensive tables of data. Two of the colour illustrations are dials with movable parts (now pasted down at their centres). Contemporary sheepskin parchment.

€ 68,000

A detailed, extensive and well-illustrated manuscript handbook of the art of navigation, probably prepared for publication but certainly never published, written by "Joan J. Plemp" whom we tentatively identify as Jan Jansz. Plemp (d. 1650), a Rotterdam official who oversaw the surveying of the city. The 178-page text, mostly in the form of questions and answers (like a catechism), is divided into 6 chapters. They provide detailed information and tables of data for making calendrical calculations; the use of the compass, including names and positions of important stars and calculating corrections for magnetic declination; tables of ephemerides giving the daily positions of the sun; determination of latitude and longitude by day and by night; calculating distances; solar declinations following Tycho Brahe; and much more. The colour illustrations include a splendid equinoctial compass sundial for keeping time at sea almost a century before Harrison's chronometer; and rectangular quadrants. The dials aid in calendrical calculations and determining latitude.The successful end of the Netherlands' Eighty-Years' War of independence from Habsburg Spain in 1648, meant that numerous sailors would be coming home from the war and many would seek work in the VOC, WIC and other commercial trading ships, which set a high value on navigational skills. Even though the Netherlands had one of the highest literacy rates in the world, the sailors who needed to or wished to learn navigation were not always well-educated, so practical guides assuming little knowledge of mathematics were essential. The parts of the two dials that were designed to rotate are now pasted down at their centres so that they do not rotate. The first leaf and last leaf have some marginal defects, affecting one word of the text and a catchword, a few bifolia have tears in the central fold, a few leaves show small browned patches, ink stains or spots in the text and the first 2 and last 10 leaves have a faint waterstain in the lower outside corner, but the manuscript remains in good condition, most leaves very good. The binding lacks most of the ties, as noted, and has a few minor stains and small tears, but it remains in good condition. An important, unpublished practical handbook of navigation, written as the Dutch reached the height of their power as commercial shippers and overseas traders, well and extensively illustrated, often in colour.